Fiber optic links can provide greater than THz bandwidths over long distances by transmitting one or more data streams at speeds in excess of 10's of Gigabits per second on a single fiber. Optical fiber offers several desirable characteristics, including low transmission loss, very compact size, light weight and relatively low cost. Nevertheless, the deployment of fiber optic cable does introduce challenges which make the installation, maintenance and operation of a fiber-based network demanding compared to the traditional copper-based network. Improved cabling and interconnect systems are required to address these challenges.
In particular, one attribute of copper-based cables which is deficient in fiber optic cables is the ability to wirelessly trace the physical locations and termination points of cables throughout a network; for example, along a cable tray or within wall and ceiling plenums. Traditional electrical tracing of copper cables is accomplished by connecting a radio frequency (RF) tone generator to one or two electrical conductors to energize the cable with a sinusoidal or square wave voltage signal in the frequency range of 500 Hz to 33 kHz. A weak electromagnetic signature at this characteristic frequency is radiated along the entire length of the wire, whereby the wire functions as an extended wire antenna in which the surrounding environment provides a common ground. This RF signal transmits through non-conductive walls, floors and ceilings with minimal signal strength attenuation and is detected by a wireless, handheld RF tone detector. A tone detector, such as the type marketed by Psiber Inc. and Test-Um Inc., typically includes a voltage probe that emits an audible tone when placed in the vicinity of a cable carrying the tone. This method of voltage tone detection is the standard for tracking electronic cables.
Electronic tone-tracing techniques are ineffective in locating fiber optic cables, as typical fiber optic cables do not incorporate the electrical conductors that are needed to transmit an RF tone. Certain types of composite fiber optic cables include conductors that are embedded within the cable jacket and are difficult to access in a non-invasive fashion. While fiber optic cables could, in principle, emit an optical signal along their entire length, in practice the optical attenuation of fiber optic cables is extremely low, typically less than 0.1 dB/km, and the leakage along its length is a small fraction of this. Optical detectors that physically clip on to fiber to produce a lossy microbend are one of the few alternatives to detect light within the fiber. As a consequence, present day optical detection techniques are unable to trace the fiber in a wireless fashion and can not be performed if the cable lies behind obstructions such as a wall, ceiling, floor or a bundle of cables.
For specialized tracing applications, composite cables with optical fiber and copper wire within a single coextensive outer jacket have been developed. However, the expense and non-standard processes required to both optically and electrically terminate, that is, add connectors to such cables, have restricted their use. Because the major component in the cost of the cable is the connector, these specialized cable assemblies are relatively costly. The injection of a suitably strong electrical signal into the cable requires that the cable jacket be physically cut or removed to gain access to the wires, potentially causing damage to the fiber optic cable and compromising its strength. This adds serious reliability concerns to the already fragile optical fiber medium.
U.S. Pat. Nos. 6,743,044, 6,905363 and 7,150,656 by ADC Telecommunications Inc. describe “tracer light” patchcords which include a pair of insulated electrical conductors within the cable jacket and utilize custom cable assemblies with dual electrical and optical connectors. The non-traditional cables and connectors only allow access to the conductors at the connectorized cable endpoints, unless the fiber optic cable jacket is partially removed by an invasive procedure. In addition, these cables are not well suited for on-site termination because they require a non-standard connectorization process wherein the individual optical fibers as well as the conductors are terminated. Therefore, standard quick termination connectors used for field connectorization are not applicable.
Alternately, U.S. Pat. Nos. 5,265,187 and 5,337400 by Morin et al. disclose a fiber optic cable distribution frame including optical connector holders with electrical circuits and LED's to enable both ends of any patchcord to be visually identified. The patchcords include internal electrical conductors providing power to the LED status indicators. Similarly, U.S. Pat. No. 5,666,453 by Dannenmann describes a fiber optic jumper cable including a pair of insulated, electrical conductors and electrically powered light emitting diodes integrated into the fiber optic connectors.
Additional implementations of composite electronic-optical cables are described in U.S. Pat. No. 6,456,768 and in UK Patent application 2354600A by Weatherly. The latter application discloses a cable consisting of an individual or pair of optical fibers with an internal metal tracing element, whereby a tracing signal may be injected at one end of the cable and detected at the other end of the cable. The tracing element is located beneath the outermost jacket. Again, an invasive approach is required to access internal electrical conductors. RFID tags have been proposed to label the endpoints of cables, and present day techniques are adequate to manually read the identification of such tags using a handheld reader brought in close proximity to tag.
The ability to trace the physical location of fiber optic cables in a convenient and low cost fashion is an increasingly important feature of interconnect systems in today's networks. Moreover, the integration of cable tracing and identification with the network's Operations Support Systems (OSS) is a key enhancement enabling the remote and automated management and inventory control of physical connections with a fiber optic network